1. Field of the Invention
This invention relates to semipermeable membranes and their use for gas separation. In one aspect, the invention relates to semipermeable membranes prepared from one or more cellulosic polymers and at least one silicon compound while in another aspect, the invention relates to the use of these membranes to separate a gaseous mixture into various fractions.
2. Description of the Prior Art
Semipermeable membranes prepared from cellulosic polymers and the use of such membranes for ultrafiltration and desalination has long been known. Over the last several decades and particularly over the last decade, these membranes have also been studied for use in separating gaseous mixtures into various fractions. For example, see Henis and Tripodi, U.S. Pat. No. 4,230,463.
Unmodified cellulose is a nonthermoplastic and an essentially insoluble material in common organic solvents. However, ether and ester derivatives of cellulose, such as ethyl cellulose and cellulose triacetate, are thermoplastic and soluble in a number of different common organic solvents and are thus not only good film and fiber formers but are also commercially important commodities.
Semipermeable membranes manufactured from modified and unmodified cellulosic polymers show, as a group, some interesting properties. For example, cellulose triacetate and cellulose diacetate have a relatively high permeability and selectivity for separating oxygen from air and carbon dioxide from natural gas. However, although these properties are relatively high compared to membranes prepared from other polymers, there still exists opportunity for further improvement.